Supplemental Oil and Gas Disclosures - Costs Incurred in Oil and Gas Property Acquisitions, Exploration and Development Activities (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	$ 35	$ 104	$ 177
Unproved	340	1,388	379
Exploration	453	973	1,678
Development	3,638	9,180	8,548
Costs incurred	4,466	11,645	10,782
Proved properties	89,069	89,852
Unproved properties	2,611	7,014
Capitalized costs, gross	91,680	96,866
Accumulated DD&A	(78,852)	(53,001)
Capitalized costs, net	12,828	43,865
United States [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	1	102	17
Unproved	313	1,221	195
Exploration	131	467	562
Development	1,957	5,301	5,435
Costs incurred	2,402	7,091	6,209
Proved properties	51,693	47,001
Unproved properties	1,824	4,151
Capitalized costs, gross	53,517	51,152
Accumulated DD&A	(48,161)	(27,205)
Capitalized costs, net	5,356	23,947
Canada [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	8
Unproved	23	141	151
Exploration	41	82	36
Development	193	846	722
Costs incurred	265	1,069	909
Proved properties	14,613	14,003
Unproved properties	234	1,090
Capitalized costs, gross	14,847	15,093
Accumulated DD&A	(13,582)	(9,653)
Capitalized costs, net	1,265	5,440
Egypt [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	25	1	35
Unproved	4	10	15
Exploration	110	193	559
Development	764	1,142	618
Costs incurred	903	1,346	1,227
Proved properties	11,296	9,895
Unproved properties	30	529
Capitalized costs, gross	11,326	10,424
Accumulated DD&A	(7,779)	(6,369)
Capitalized costs, net	3,547	4,055
Australia [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	1	1
Unproved		16	(10)
Exploration	31	137	179
Development	101	914	996
Costs incurred	133	1,068	1,165
Proved properties		8,289
Unproved properties		549
Capitalized costs, gross		8,838
Accumulated DD&A		(3,198)
Capitalized costs, net		5,640
North Sea [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved			125
Unproved			17
Exploration	111	84	278
Development	623	971	635
Costs incurred	734	1,055	1,055
Proved properties	11,266	10,463
Unproved properties	471	672
Capitalized costs, gross	11,737	11,135
Accumulated DD&A	(9,129)	(6,375)
Capitalized costs, net	2,608	4,760
Argentina [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Unproved			11
Exploration		9	42
Development		6	142
Costs incurred		15	195
Other International [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Exploration	29	1	22
Costs incurred	29	1	$ 22
Proved properties	201	201
Unproved properties	52	23
Capitalized costs, gross	253	224
Accumulated DD&A	(201)	(201)
Capitalized costs, net	$ 52	$ 23